The present invention relates to body implantable treatment devices, and more particularly to stents and other prostheses intended for fixation in body lumens especially including the esophagus.
Carcinomas in the esophagus lead to progressive dysphagia, i.e. difficulty in swallowing, and the inability to swallow liquids in the most severe cases. While surgical removal is sometimes effective, the majority of patients have tumors that can not be surgically removed. Repeated dilations of the esophagus provide only temporary relief.
Difficult or refractory cases often are treated by intubation using rigid plastic prostheses, or laser therapy with an Nd:YAG laser. These techniques, while often effective, have disadvantages. Rigid plastic protheses are large, for example having a diameter of 10-12 mm and larger (25-29 mm) outer end flanges. Placement of rigid plastic stents is traumatic, and too frequently causes perforation of the esophageal wall. These protheses further are subject to migration, obstruction with food or tumor ingrowth, and late pressure necrosis.
Laser therapy is expensive, typically requiring several treatment sessions. Tumor recurrence is frequent, in the range of 30-40 percent. Submucosal tumors, and certain pulmonary and breast tumors causing dysphagia by esophageal compression, can not be treated by laser therapy.
The search for a more suitable prosthesis has lead to experiments with Gianturco stents, also known as Z-stents. U.S. Pat. No. 4,800,882 (Gianturco) describes such a device employed as an endovascular stent. Such stents for the esophagus have been constructed of 0.018 inch stainless steel wire, and provided with a silicone cover to inhibit tumor ingrowth. It was found necessary, however, to provide a distal silicone bumper to prevent trauma to the esophageal mucosa.
Self-expanding mesh stents also have been considered for use as esophageal prostheses. U.S. Pat. No. 4,655,771 (Wallsten) discloses a mesh stent as a flexible tubular braided structure formed of helically wound thread elements. Mesh stents appear unlikely to lead to pressure necrosis of the esophageal wall. With its inherent pliability the mesh stent, as compared to a rigid plastic stent, is insertable with much less trauma to the patient. Further, the stent can mold itself to and firmly fix itself against the esophageal wall, to resist migration. However, the stent is subject to tumor ingrowth because of the spaces between adjacent filaments.
A further difficulty with self-expanding stents, concerns their accurate placement and deployment. Typically a tube surrounds the self-expanding stent and radially compresses the stent into a reduced-radius delivery configuration. With the stent positioned at a treatment site, the outer tube is axially withdrawn, permitting the stent to radially self-expand. However, the larger size of an esophageal stent (as compared to biliary and vascular applications, for example) gives rise to substantial friction at the stent/outer tubing interface. As a result, it is difficult to precisely maintain the position of the stent during deployment, and practically impossible to retract the stent after partial deployment.
Therefore, it is an object of the present invention to provide a stent delivery device including exterior tubing surrounding the stent and movable axially to release the stent for radial self-expansion without a tendency in the stent to follow the axial movement of the exterior tubing.
Another object is to provide a stent deployment device capable of retracting a radially self-expanding stent for repositioning of the stent, even though the stent has been partially deployed and is radially expanded over the majority of its axial length.
Another object is to provide a device for delivering and deploying a prostheses to a treatment site within a body lumen, with means for dilating the body lumen at the treatment site prior to stent deployment.
A further object of the invention is to provide a radially self-expanding stent including a freely radially self-expanding fixation region in combination with a barrier region to inhibit tumor ingrowth.
Yet another object is to provide an esophageal prostheses deployable with reduced trauma to the patient, having more resistance to migration, and providing a barrier to tumor ingrowth as effective as conventional rigid plastic prostheses.
To achieve these and other objects, there is provided an apparatus for deploying a radially self-expanding stent within a body lumen. The apparatus includes a stent confining means for elastically compressing a radially self-expanding stent into a delivery configuration in which the self-expanding stent has a reduced radius along its entire axial length. The apparatus includes an elongate and flexible stent delivery device having a proximal end, a distal end and a distal region near the distal end. The distal region is used in delivering the radially self-expanding stent into a body lumen, and in positioning at a treatment site within the body lumen with the stent surrounding the delivery device along the distal region. The proximal end of the delivery device remains outside of the body. An axial restraining means is disposed along the distal region of the delivery device. A control means is operably associated with the delivery device and the confining means. The control means moves the confining means axially relative to the delivery device toward and away from a confinement position in which the confining means compresses the self-expanding stent into the delivery configuration, and urges the stent into a surface engagement with the axial restraining means. The restraining means, due to the surface engagement, tends to maintain the self-expanding stent axially aligned with the deployment device as the confining means is moved axially away from the confinement position to release the stent for radial self-expansion.
Preferably the stent delivery device is an elongate and flexible length of interior tubing, with a central lumen for accommodating a guidewire. The stent confining means can be an elongate and flexible length of tubing, having a lumen for containing the interior tubing. The second (or outer) tubing surrounds the stent to confine it.
The preferred axial restraining means is a low durometer sleeve surrounding the interior tubing along the distal region. If desired, an adhesive can be applied to an exterior surface of the sleeve. Alternatively, the axial restraining means can consist of several elongate strips disposed along the distal region, with adhesive applied to radially outward surfaces of the strips, if desired.
In either event, so long as the exterior tubing surrounds the stent to radially compress the stent, it also maintains the stent in surface engagement with the sleeve or strips. As the exterior tubing is axially withdrawn to allow part of the stent to radially self-expand, the rest of the stent remains confined against the sleeve or the strips. As a result, the stent does not travel axially with the exterior tubing. Rather, the stent remains substantially fixed in the axial direction with respect to the interior tubing. This structure affords several advantages. First, the interior tubing can be used as a means to positively maintain the radially self-expanding stent in the desired axial position during deployment. The interior tubing can itself be employed as a reliable indicator of stent position, both prior to and during deployment. Further, should the need arise to retract the stent after a partial deployment, the outer tubing can be moved back into the confinement position, without tending to carry the stent along with it.
Another aspect of the present invention is a device for fixation in a body lumen. The device includes a tubular stent of open weave construction having a predetermined normal configuration. The stent is radially compressible to a reduced-radius configuration to facilitate an axial insertion of the stent into a body lumen for delivery to a treatment site within the body lumen. A continuous film is formed axially along the stent and circumscribes the stent over a barrier region of the stent. The continuous film substantially prevents growth of tissue through the stent along the barrier region. A portion of the stent is substantially free of the continuous film to provide a fixation region of the stent for positively fixing the stent within the body lumen at the treatment site. Fixation is achieved by radial expansion of the stent into a surface engagement with a tissue wall segment defining the body lumen.
The preferred stent comprises a mesh formed of braided helical strands. The fixation region can comprise a proximal cuff and a distal cuff, with the barrier region being a medial sleeve of the stent positioned between the cuffs. Also, the barrier region preferably has a diameter less than the fixation region diameter when the stent is in its normal or relaxed configuration. A preferred material for the film is silicone. When properly controlled as to thickness, the silicone film provides a gradual self-expansion. More particularly, while the fixation region self-expands virtually instantaneously upon release of the stent, the medial barrier region, upon encountering a tumor or other striction, can take up to 24 hours to achieve a substantially complete radial self-expansion against the tumor.
This feature is particularly advantageous in connection with treating esophageal strictures, where tissue at the stricture may be severely weakened, and where normal convulsions of the esophagus tend to cause stent migration. More particularly, the rapidly expanding fixation regions contact normal esophageal tissue on either side of a stricture, and are sufficiently pliable to adjust to esophageal convulsions. Meanwhile, the barrier region of the stent experiences a gradual radial expansion, thus causing minimal disruption to tissue along the stricture.
A further feature of the invention is a system for treating a stricture within a body lumen. The system includes a radially self-expanding stent, and an elongate and flexible stent delivery device having a proximal end and distal end. The device further has a distal region for delivering the radially self-expanding stent into the body lumen and positioning the stent at a treatment site within the body lumen, with the stent surrounding the delivery device along the distal region. A first elongate and flexible length of tubing, having a lumen running the length of thereof, contains the stent delivery device within the lumen. The first tubing also elastically compresses the stent into a delivery configuration in which the stent has a reduced radius along its entire axial length. The first tubing is movable proximally relative to the delivery device and the stent, to allow the stent to radially self-expand into a surface engagement with body tissue defining the lumen. A distal tip is provided at the distal end of the stent delivery device for initially dilating a stricture at the treatment site. An enlargement feature is provided near the distal end of the stent delivery device. The enlargement feature has a diameter substantially equal to an interior diameter of the first tubing. The enlargement feature further has a distal transition region that diverges proximally from the tip to a mid-portion of the enlargement feature. The transition region further dilates the stricture to facilitate a positioning of the distal region of the first tubing along the stricture.
Preferably the distal region of the delivery device has a diameter less than the diameter of the enlargement feature mid-portion, and the enlargement feature further includes proximal transition region that converges in the proximal direction from the enlargement feature mid-portion. The proximal transition region facilitates withdrawal of the delivery device after deployment of the stent.
Thus, in accordance with the present invention, a radially self-expanding stent can be positioned accurately at a desired treatment site within a body lumen, based on an accurate positioning of the interior tubing or other stent delivery means. The stent may be allowed to radially self-expand over the majority of its axial length, and yet be retracted if necessary or desired, all while its axial position with respect to the delivery tool is maintained.